Liquid crystal display devices have a small thickness, low weight, and low power consumption and therefore are widely used as display devices for televisions, personal computers, and PDAs. In particular, in recent years, the liquid crystal display devices have been increasingly upsized as typified by liquid crystal display devices for televisions. A multi-domain vertical alignment (MVA) mode which enables high-yield manufacture in spite of large areas and which provides a wide viewing angle is preferably used for upsizing. The multi-domain vertical alignment mode can provide higher contrast ratio as compared to a conventional TN (twisted nematic) mode because liquid crystal molecules are aligned perpendicularly to a substrate surface when no voltage is applied to a liquid crystal layer.
In the MVA mode, the tilt direction of liquid crystal molecules is not controlled by an alignment film but is determined by the influence of protrusions (ribs) made of an insulating material. Thus, the alignment film need not be subjected to an alignment treatment step and static electricity or dust due to rubbing or the like is not caused; hence, a cleaning step or the like subsequent to alignment treatment is unnecessary. Furthermore, the variation in pretilt of the liquid crystal molecules is small, which is effective for the simplification of a process, an increase in yield, and cost reduction.
In the MVA mode, although alignment treatment is not necessary, a base film corresponding to the alignment film needs to be formed. The base film is preferably eliminated in consideration of the influence of the variation in thickness of the base film or the contamination of dust on the alignment of the liquid crystal molecules and in consideration of the increase in number of manufacturing steps and capital investment for forming the base film.
In recent years, in order to cope with this, the following technique has been attracting attention: a pretilt angle-imparting technique in which a polymer layer is formed in such a way that a liquid crystal composition prepared by mixing a liquid crystal with a polymerizable component (hereinafter simply referred to as “monomer or the like”) such as a monomer, an oligomer, or the like is sealed between substrates and the monomer or the like is polymerized in such a state that molecules of the liquid crystal are tilted by applying a voltage between the substrates (refer to, for example, Patent Literatures 1 to 8). The liquid crystal has a predetermined pretilt angle under the influence of the polymer layer even after the applied voltage is removed. Therefore, the tilt direction of the liquid crystal molecules is maintained even though there is no alignment film. Incidentally, the monomer or the like is polymerized by heating or light (for example, ultraviolet ray) irradiation.